Fridman, via his DEA Deutsche Erdoel AG unit, is buying Sierra Oil & Gas from a group of private-equity owners, according to a statement from the company. DEA didn’t disclose financial terms, but a person familiar with the negotiations put the value of the deal at around $500 million. The transaction, which is set to become the largest upstream acquisition in Mexico since the liberalization of its petroleum sector in 2013, signals that energy groups remain interested despite the left-wing policies planned by new President Andres Manuel Lopez Obrador.